1. Field of the Invention
The invention concerns lateral isolation of active areas of a semiconductor substrate by shallow trenches.
2. Description of the Related Art
Lateral isolation techniques are evolving against a background of reducing dimensions and increasing density in the field of microelectronics. The person skilled in the art already knows techniques based on localised oxidation ("LOCOS"). In a technique of this kind, oxide is grown by a thermal process in an opening intended to form the isolating structure. However, the person skilled in the art also knows that a structure of this kind spreads laterally in a so-called "beak" shape causing widening of the isolation area and shrinking of the active area. At present the length of the beak can be reduced by a large number of technical operations. Nevertheless, this technique is subject to limitations which cannot be overcome at present because the technique leads to thinning of the insulative oxide in narrow openings.
The person skilled in the art knows different isolation techniques which consists in filling shallow trenches with an insulative material. The person skilled in the art usually calls this technique the "BOX" technique or "Shallow Trench Isolation (STI)". This technique has been the subject of considerable research and many publications over a number of years and has to date been developed to only a very limited extent because of its technological complexity.